Other than direct sound that arrives directly from a sound source, sound that is reflected by a wall, a floor, a ceiling, and the like to arrive later than the direct sound is referred to as “reverberation”. When a sound source is voice, large reverberation makes phonemes unclear to make it difficult to hear the voice. Signal processing technology for removing reverberation from voice collected by a microphone to make it easier to hear the voice has been developed.
One example of the proposed technology is to use an observation signal collected by a microphone to estimate an inverse filter having inverse characteristics to transfer characteristics from a sound source to the microphone, and perform inverse filtering on the observation signal to remove reverberation. Another proposed technology is to estimate a reverberation removal filter from an observation signal on the basis of an autoregressive model representing a current observation signal as a signal obtained by adding a sound source signal to a signal obtained by applying a reverberation removal filter to past observation signals having a predetermined delay, and apply the reverberation removal filter to the observation signal to remove reverberation.
In the conventional technologies, however, the accuracy of reverberation removal may decrease due to mismatching of the model and physical phenomena, use of an approximate filter, and other such reasons.